It took Democrats about five seconds to trigger the parliamentary move that forced the Senate into a rare closed session this week, but it was more than a year in the planning.

The final decision to employ the tactic, which infuriated Republicans and exacerbated partisan animosity, was made in the Democratic leader's second-floor Capitol office Monday night, in a small gathering of his lieutenants. Minority Leader Harry M. Reid (Nev.) considered the strategy to be so sensitive that only four of his colleagues knew what he intended when he entered the Senate chamber at 2:25 p.m. Tuesday, party aides said yesterday.

Reid invoked Senate Rule 21, which allows any senator to order all non-members from the chamber. The rule's existence was widely known, and closed sessions had been held by bipartisan agreement as recently as 1999, regarding President Bill Clinton's impeachment. But the notion of one party springing the rule on the other party without warning was so alien that senators could not cite a previous example. Republican leaders quickly denounced it as a stunt, an affront, a trust-killing slap in the face.

Reid's aides said yesterday that their boss decided on the dramatic, attention-grabbing ploy because he was weary of GOP foot-dragging on a promised inquiry by the Senate intelligence committee into the Bush administration's handling of prewar intelligence on Iraq. "We'd had enough press conferences and requests, public and private," Reid spokesman Jim Manley said. "Now it was time to act."

But Reid did not have to start from scratch. His predecessor, former Democratic leader Thomas A. Daschle (S.D.), had considered going into closed session to discuss intelligence use and to spur the inquiry launched in early 2004. But he wanted the cooperation of Majority Leader Bill Frist (R-Tenn.).

"For the past couple of years, Senator Frist and I had agreed to hold an executive session," Daschle said yesterday. But Frist "kept putting it off." Daschle said several Democratic senators "threatened to do it over his opposition during that time, but it never got to that point."

Daschle's staff researched exactly how Rule 21 might be used, aides said, and its findings were at Reid's fingertips when he convened the weekly meeting of his leadership team at 6:15 p.m. Monday. Present were party Whip Richard J. Durbin (Ill.), conference Secretary Debbie Stabenow (Mich.) and campaign committee Chairman Charles E. Schumer (N.Y.). In an interview yesterday, Schumer said the group decided on the closed session out of frustration over the Bush administration's "stonewalling" and their anger over the White House's failure to apologize after senior aide I. Lewis "Scooter" Libby was indicted Friday on perjury charges connected to claims that prewar intelligence on Iraq was manipulated.

"There's nothing more poisonous to a democracy than the refusal to listen to facts," Schumer said.

Reid obtained an enthusiastic endorsement of the plan from Sen. John D. Rockefeller IV (W.Va.), the intelligence committee's top Democrat, Manley said. But even though Reid attended a private lunch for all 44 Democratic senators Tuesday, he did not mention the plan to anyone else before springing his surprise on the Senate floor moments later. If word had leaked, Manley said, Republicans could have kept the Senate in a "quorum call" that would have prevented Reid from speaking.

Frist was indignant. As Senate aides shooed visitors from the galleries and shut down C-SPAN's cameras, Frist told reporters that Reid's leadership team resorted to a "political stunt" because it had no convictions, principles or ideas. "For the next year and a half, I can't trust Senator Reid," he said.

When the chamber reopened about two hours later, Frist named a bipartisan task force to report on the intelligence committee's progress on the long-awaited inquiry into how the administration used prewar intelligence. In a floor speech, Committee Chairman Pat Roberts (R-Kan.) said the closed session was unnecessary because "just yesterday" his staff was working with Democratic staffers on plans "to complete our work" on the inquiry. Democrats said they saw no evidence of movement.

In an interview yesterday, a still-smoldering Frist said that "by sitting down in a civil way with Roberts, Rockefeller, Reid and Frist, we would have come exactly to what we did" on Tuesday.

But Democrats were unapologetic, saying their tactic spurred the Republicans to action and energized Democratic activists tired of seeing their party pushed around.

"My phones have been ringing off the hook" at the Democratic Senatorial Campaign Committee, Schumer said. "It has played far better than we had thought."